[PATCH v3 net-next 0/7] rfs: use high-order allocations for hash tables

[PATCH v3 net-next 0/7] rfs: use high-order allocations for hash tables

[Eric Dumazet]

This series adds rps_tag_ptr which encodes both a pointer
and a size of a power-of-two hash table in a single long word.

RFS hash tables (global and per rx-queue) are converted to rps_tag_ptr.

This removes a cache line miss, and allows high-order allocations.

The global hash table can benefit from huge pages.

v2 and v3: address various kernel bots reports.

Eric Dumazet (7):
  net: add rps_tag_ptr type and helpers
  net-sysfs: remove rcu field from 'struct rps_sock_flow_table'
  net-sysfs: add rps_sock_flow_table_mask() helper
  net-sysfs: use rps_tag_ptr and remove metadata from
    rps_sock_flow_table
  net-sysfs: get rid of rps_dev_flow_lock
  net-sysfs: remove rcu field from 'struct rps_dev_flow_table'
  net-sysfs: use rps_tag_ptr and remove metadata from rps_dev_flow_table

 Documentation/networking/scaling.rst | 13 ++--
 include/net/hotdata.h                |  5 +-
 include/net/netdev_rx_queue.h        |  3 +-
 include/net/rps-types.h              | 24 +++++++
 include/net/rps.h                    | 49 ++++++---------
 net/core/dev.c                       | 61 +++++++++++-------
 net/core/net-sysfs.c                 | 83 ++++++++++--------------
 net/core/sysctl_net_core.c           | 94 +++++++++++++++-------------
 8 files changed, 180 insertions(+), 152 deletions(-)
 create mode 100644 include/net/rps-types.h

-- 
2.53.0.473.g4a7958ca14-goog

[PATCH v3 net-next 1/7] net: add rps_tag_ptr type and helpers

[Eric Dumazet]

Add a new rps_tag_ptr type to encode a pointer and a size
to a power-of-two table.

Three helpers are added converting an rps_tag_ptr to:

1) A log of the size.

2) A mask : (size - 1).

3) A pointer to the array.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/rps-types.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 include/net/rps-types.h

diff --git a/include/net/rps-types.h b/include/net/rps-types.h
new file mode 100644
index 0000000000000000000000000000000000000000..6b90a66866c1f75dae768bed84a4eeb9ffb5fc1a
--- /dev/null
+++ b/include/net/rps-types.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_RPS_TYPES_H
+#define _NET_RPS_TYPES_H
+
+/* Define a rps_tag_ptr:
+ * Low order 5 bits are used to store the ilog2(size) of an RPS table.
+ */
+typedef unsigned long rps_tag_ptr;
+
+static inline u8 rps_tag_to_log(rps_tag_ptr tag_ptr)
+{
+	return tag_ptr & 31U;
+}
+
+static inline u32 rps_tag_to_mask(rps_tag_ptr tag_ptr)
+{
+	return (1U << rps_tag_to_log(tag_ptr)) - 1;
+}
+
+static inline void *rps_tag_to_table(rps_tag_ptr tag_ptr)
+{
+	return (void *)(tag_ptr & ~31UL);
+}
+#endif /* _NET_RPS_TYPES_H */
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 1/7] net: add rps_tag_ptr type and helpers

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Add a new rps_tag_ptr type to encode a pointer and a size
> to a power-of-two table.
>
> Three helpers are added converting an rps_tag_ptr to:
>
> 1) A log of the size.
>
> 2) A mask : (size - 1).
>
> 3) A pointer to the array.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 2/7] net-sysfs: remove rcu field from 'struct rps_sock_flow_table'

[Eric Dumazet]

Removing rcu_head (and @mask in a following patch)
will allow a power-of-two allocation and thus high-order
allocation for better performance.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/rps.h          | 1 -
 net/core/sysctl_net_core.c | 4 +++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/rps.h b/include/net/rps.h
index f1794cd2e7fb32a36bde9959fab651663ab190fd..32cfa250d9f931b8ab1c94e0410d0820bb9c999f 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -60,7 +60,6 @@ struct rps_dev_flow_table {
  * meaning we use 32-6=26 bits for the hash.
  */
 struct rps_sock_flow_table {
-	struct rcu_head	rcu;
 	u32		mask;
 
 	u32		ents[] ____cacheline_aligned_in_smp;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 03aea10073f003b0339884ee0f40b8c96d7d22e2..0b659c932cffef45e05207890b8187d64ae3c85a 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -147,6 +147,7 @@ static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 	};
 	struct rps_sock_flow_table *orig_sock_table, *sock_table;
 	static DEFINE_MUTEX(sock_flow_mutex);
+	void *tofree = NULL;
 
 	mutex_lock(&sock_flow_mutex);
 
@@ -193,13 +194,14 @@ static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 			if (orig_sock_table) {
 				static_branch_dec(&rps_needed);
 				static_branch_dec(&rfs_needed);
-				kvfree_rcu(orig_sock_table, rcu);
+				tofree = orig_sock_table;
 			}
 		}
 	}
 
 	mutex_unlock(&sock_flow_mutex);
 
+	kvfree_rcu_mightsleep(tofree);
 	return ret;
 }
 #endif /* CONFIG_RPS */
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 2/7] net-sysfs: remove rcu field from 'struct rps_sock_flow_table'

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Removing rcu_head (and @mask in a following patch)
> will allow a power-of-two allocation and thus high-order
> allocation for better performance.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 3/7] net-sysfs: add rps_sock_flow_table_mask() helper

[Eric Dumazet]

In preparation of the following patch, abstract access
to the @mask field in 'struct rps_sock_flow_table'.

Also cleanup rps_sock_flow_sysctl() a bit :

- Rename orig_sock_table to o_sock_table.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/rps.h          | 11 ++++++++---
 net/core/dev.c             |  4 +++-
 net/core/sysctl_net_core.c | 19 ++++++++++---------
 3 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/include/net/rps.h b/include/net/rps.h
index 32cfa250d9f931b8ab1c94e0410d0820bb9c999f..82cdffdf3e6b0035e7ceeb130b5b4ac19772e46c 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -60,18 +60,23 @@ struct rps_dev_flow_table {
  * meaning we use 32-6=26 bits for the hash.
  */
 struct rps_sock_flow_table {
-	u32		mask;
+	u32		_mask;
 
 	u32		ents[] ____cacheline_aligned_in_smp;
 };
 #define	RPS_SOCK_FLOW_TABLE_SIZE(_num) (offsetof(struct rps_sock_flow_table, ents[_num]))
 
+static inline u32 rps_sock_flow_table_mask(const struct rps_sock_flow_table *table)
+{
+	return table->_mask;
+}
+
 #define RPS_NO_CPU 0xffff
 
 static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
 					u32 hash)
 {
-	unsigned int index = hash & table->mask;
+	unsigned int index = hash & rps_sock_flow_table_mask(table);
 	u32 val = hash & ~net_hotdata.rps_cpu_mask;
 
 	/* We only give a hint, preemption can change CPU under us */
@@ -129,7 +134,7 @@ static inline void _sock_rps_delete_flow(const struct sock *sk)
 	rcu_read_lock();
 	table = rcu_dereference(net_hotdata.rps_sock_flow_table);
 	if (table) {
-		index = hash & table->mask;
+		index = hash & rps_sock_flow_table_mask(table);
 		if (READ_ONCE(table->ents[index]) != RPS_NO_CPU)
 			WRITE_ONCE(table->ents[index], RPS_NO_CPU);
 	}
diff --git a/net/core/dev.c b/net/core/dev.c
index 1cf3ad840697ed93a6c4cc5163aae514fda90eff..de70ef784d6363b3af4f9279e107647c90f5af19 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5112,12 +5112,14 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 	if (flow_table && sock_flow_table) {
 		struct rps_dev_flow *rflow;
 		u32 next_cpu;
+		u32 flow_id;
 		u32 ident;
 
 		/* First check into global flow table if there is a match.
 		 * This READ_ONCE() pairs with WRITE_ONCE() from rps_record_sock_flow().
 		 */
-		ident = READ_ONCE(sock_flow_table->ents[hash & sock_flow_table->mask]);
+		flow_id = hash & rps_sock_flow_table_mask(sock_flow_table);
+		ident = READ_ONCE(sock_flow_table->ents[flow_id]);
 		if ((ident ^ hash) & ~net_hotdata.rps_cpu_mask)
 			goto try_rps;
 
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 0b659c932cffef45e05207890b8187d64ae3c85a..cfbe798493b5789dc8baedf9dcbe9c20918e2ba6 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -145,16 +145,17 @@ static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 		.maxlen = sizeof(size),
 		.mode = table->mode
 	};
-	struct rps_sock_flow_table *orig_sock_table, *sock_table;
+	struct rps_sock_flow_table *o_sock_table, *sock_table;
 	static DEFINE_MUTEX(sock_flow_mutex);
 	void *tofree = NULL;
 
 	mutex_lock(&sock_flow_mutex);
 
-	orig_sock_table = rcu_dereference_protected(
+	o_sock_table = rcu_dereference_protected(
 					net_hotdata.rps_sock_flow_table,
 					lockdep_is_held(&sock_flow_mutex));
-	size = orig_size = orig_sock_table ? orig_sock_table->mask + 1 : 0;
+	size = o_sock_table ? rps_sock_flow_table_mask(o_sock_table) + 1 : 0;
+	orig_size = size;
 
 	ret = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 
@@ -165,6 +166,7 @@ static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 				mutex_unlock(&sock_flow_mutex);
 				return -EINVAL;
 			}
+			sock_table = o_sock_table;
 			size = roundup_pow_of_two(size);
 			if (size != orig_size) {
 				sock_table =
@@ -175,26 +177,25 @@ static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 				}
 				net_hotdata.rps_cpu_mask =
 					roundup_pow_of_two(nr_cpu_ids) - 1;
-				sock_table->mask = size - 1;
-			} else
-				sock_table = orig_sock_table;
+				sock_table->_mask = size - 1;
+			}
 
 			for (i = 0; i < size; i++)
 				sock_table->ents[i] = RPS_NO_CPU;
 		} else
 			sock_table = NULL;
 
-		if (sock_table != orig_sock_table) {
+		if (sock_table != o_sock_table) {
 			rcu_assign_pointer(net_hotdata.rps_sock_flow_table,
 					   sock_table);
 			if (sock_table) {
 				static_branch_inc(&rps_needed);
 				static_branch_inc(&rfs_needed);
 			}
-			if (orig_sock_table) {
+			if (o_sock_table) {
 				static_branch_dec(&rps_needed);
 				static_branch_dec(&rfs_needed);
-				tofree = orig_sock_table;
+				tofree = o_sock_table;
 			}
 		}
 	}
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 3/7] net-sysfs: add rps_sock_flow_table_mask() helper

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> In preparation of the following patch, abstract access
> to the @mask field in 'struct rps_sock_flow_table'.
>
> Also cleanup rps_sock_flow_sysctl() a bit :
>
> - Rename orig_sock_table to o_sock_table.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 4/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_sock_flow_table

[Eric Dumazet]

Instead of storing the @mask at the beginning of rps_sock_flow_table,
use 5 low order bits of the rps_tag_ptr to store the log of the size.

This removes a potential cache line miss to fetch @mask.

More importantly, we can switch to vmalloc_huge() without wasting memory.

Tested with:

numactl --interleave=all bash -c "echo 4194304 >/proc/sys/net/core/rps_sock_flow_entries"

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 Documentation/networking/scaling.rst | 13 ++--
 include/net/hotdata.h                |  5 +-
 include/net/rps.h                    | 42 ++++++-------
 net/core/dev.c                       | 12 ++--
 net/core/sysctl_net_core.c           | 89 +++++++++++++++-------------
 5 files changed, 86 insertions(+), 75 deletions(-)

diff --git a/Documentation/networking/scaling.rst b/Documentation/networking/scaling.rst
index 0023afa530ec166bb13558318053ff5ed0906b71..6c261eb48845a40516f201233df13694863ee8cd 100644
--- a/Documentation/networking/scaling.rst
+++ b/Documentation/networking/scaling.rst
@@ -403,16 +403,21 @@ Both of these need to be set before RFS is enabled for a receive queue.
 Values for both are rounded up to the nearest power of two. The
 suggested flow count depends on the expected number of active connections
 at any given time, which may be significantly less than the number of open
-connections. We have found that a value of 32768 for rps_sock_flow_entries
-works fairly well on a moderately loaded server.
+connections. We have found that a value of 65536 for rps_sock_flow_entries
+works fairly well on a moderately loaded server. Big servers might
+need 1048576 or even higher values.
+
+On a NUMA host it is advisable to spread rps_sock_flow_entries on all nodes.
+
+numactl --interleave=all bash -c "echo 1048576 >/proc/sys/net/core/rps_sock_flow_entries"
 
 For a single queue device, the rps_flow_cnt value for the single queue
 would normally be configured to the same value as rps_sock_flow_entries.
 For a multi-queue device, the rps_flow_cnt for each queue might be
 configured as rps_sock_flow_entries / N, where N is the number of
-queues. So for instance, if rps_sock_flow_entries is set to 32768 and there
+queues. So for instance, if rps_sock_flow_entries is set to 131072 and there
 are 16 configured receive queues, rps_flow_cnt for each queue might be
-configured as 2048.
+configured as 8192.
 
 
 Accelerated RFS
diff --git a/include/net/hotdata.h b/include/net/hotdata.h
index 6632b1aa7584821fd4ab42163b77dfff6732a45e..62534d1f3c707038cd6b805ccc1889e7709d999d 100644
--- a/include/net/hotdata.h
+++ b/include/net/hotdata.h
@@ -6,6 +6,9 @@
 #include <linux/types.h>
 #include <linux/netdevice.h>
 #include <net/protocol.h>
+#ifdef CONFIG_RPS
+#include <net/rps-types.h>
+#endif
 
 struct skb_defer_node {
 	struct llist_head	defer_list;
@@ -33,7 +36,7 @@ struct net_hotdata {
 	struct kmem_cache	*skbuff_fclone_cache;
 	struct kmem_cache	*skb_small_head_cache;
 #ifdef CONFIG_RPS
-	struct rps_sock_flow_table __rcu *rps_sock_flow_table;
+	rps_tag_ptr		rps_sock_flow_table;
 	u32			rps_cpu_mask;
 #endif
 	struct skb_defer_node __percpu *skb_defer_nodes;
diff --git a/include/net/rps.h b/include/net/rps.h
index 82cdffdf3e6b0035e7ceeb130b5b4ac19772e46c..dee930d9dd38e0e975e78d938bc7adc96048b724 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -8,6 +8,7 @@
 #include <net/hotdata.h>
 
 #ifdef CONFIG_RPS
+#include <net/rps-types.h>
 
 extern struct static_key_false rps_needed;
 extern struct static_key_false rfs_needed;
@@ -60,45 +61,38 @@ struct rps_dev_flow_table {
  * meaning we use 32-6=26 bits for the hash.
  */
 struct rps_sock_flow_table {
-	u32		_mask;
-
-	u32		ents[] ____cacheline_aligned_in_smp;
+	u32	ent;
 };
-#define	RPS_SOCK_FLOW_TABLE_SIZE(_num) (offsetof(struct rps_sock_flow_table, ents[_num]))
-
-static inline u32 rps_sock_flow_table_mask(const struct rps_sock_flow_table *table)
-{
-	return table->_mask;
-}
 
 #define RPS_NO_CPU 0xffff
 
-static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
-					u32 hash)
+static inline void rps_record_sock_flow(rps_tag_ptr tag_ptr, u32 hash)
 {
-	unsigned int index = hash & rps_sock_flow_table_mask(table);
+	unsigned int index = hash & rps_tag_to_mask(tag_ptr);
 	u32 val = hash & ~net_hotdata.rps_cpu_mask;
+	struct rps_sock_flow_table *table;
 
 	/* We only give a hint, preemption can change CPU under us */
 	val |= raw_smp_processor_id();
 
+	table = rps_tag_to_table(tag_ptr);
 	/* The following WRITE_ONCE() is paired with the READ_ONCE()
 	 * here, and another one in get_rps_cpu().
 	 */
-	if (READ_ONCE(table->ents[index]) != val)
-		WRITE_ONCE(table->ents[index], val);
+	if (READ_ONCE(table[index].ent) != val)
+		WRITE_ONCE(table[index].ent, val);
 }
 
 static inline void _sock_rps_record_flow_hash(__u32 hash)
 {
-	struct rps_sock_flow_table *sock_flow_table;
+	rps_tag_ptr tag_ptr;
 
 	if (!hash)
 		return;
 	rcu_read_lock();
-	sock_flow_table = rcu_dereference(net_hotdata.rps_sock_flow_table);
-	if (sock_flow_table)
-		rps_record_sock_flow(sock_flow_table, hash);
+	tag_ptr = READ_ONCE(net_hotdata.rps_sock_flow_table);
+	if (tag_ptr)
+		rps_record_sock_flow(tag_ptr, hash);
 	rcu_read_unlock();
 }
 
@@ -125,6 +119,7 @@ static inline void _sock_rps_record_flow(const struct sock *sk)
 static inline void _sock_rps_delete_flow(const struct sock *sk)
 {
 	struct rps_sock_flow_table *table;
+	rps_tag_ptr tag_ptr;
 	u32 hash, index;
 
 	hash = READ_ONCE(sk->sk_rxhash);
@@ -132,11 +127,12 @@ static inline void _sock_rps_delete_flow(const struct sock *sk)
 		return;
 
 	rcu_read_lock();
-	table = rcu_dereference(net_hotdata.rps_sock_flow_table);
-	if (table) {
-		index = hash & rps_sock_flow_table_mask(table);
-		if (READ_ONCE(table->ents[index]) != RPS_NO_CPU)
-			WRITE_ONCE(table->ents[index], RPS_NO_CPU);
+	tag_ptr = READ_ONCE(net_hotdata.rps_sock_flow_table);
+	if (tag_ptr) {
+		index = hash & rps_tag_to_mask(tag_ptr);
+		table = rps_tag_to_table(tag_ptr);
+		if (READ_ONCE(table[index].ent) != RPS_NO_CPU)
+			WRITE_ONCE(table[index].ent, RPS_NO_CPU);
 	}
 	rcu_read_unlock();
 }
diff --git a/net/core/dev.c b/net/core/dev.c
index de70ef784d6363b3af4f9279e107647c90f5af19..d4837b058b2ff02e94f9590e310edbcb06dad0f2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5075,9 +5075,9 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		       struct rps_dev_flow **rflowp)
 {
-	const struct rps_sock_flow_table *sock_flow_table;
 	struct netdev_rx_queue *rxqueue = dev->_rx;
 	struct rps_dev_flow_table *flow_table;
+	rps_tag_ptr global_tag_ptr;
 	struct rps_map *map;
 	int cpu = -1;
 	u32 tcpu;
@@ -5108,8 +5108,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 	if (!hash)
 		goto done;
 
-	sock_flow_table = rcu_dereference(net_hotdata.rps_sock_flow_table);
-	if (flow_table && sock_flow_table) {
+	global_tag_ptr = READ_ONCE(net_hotdata.rps_sock_flow_table);
+	if (flow_table && global_tag_ptr) {
+		struct rps_sock_flow_table *sock_flow_table;
 		struct rps_dev_flow *rflow;
 		u32 next_cpu;
 		u32 flow_id;
@@ -5118,8 +5119,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		/* First check into global flow table if there is a match.
 		 * This READ_ONCE() pairs with WRITE_ONCE() from rps_record_sock_flow().
 		 */
-		flow_id = hash & rps_sock_flow_table_mask(sock_flow_table);
-		ident = READ_ONCE(sock_flow_table->ents[flow_id]);
+		flow_id = hash & rps_tag_to_mask(global_tag_ptr);
+		sock_flow_table = rps_tag_to_table(global_tag_ptr);
+		ident = READ_ONCE(sock_flow_table[flow_id].ent);
 		if ((ident ^ hash) & ~net_hotdata.rps_cpu_mask)
 			goto try_rps;
 
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index cfbe798493b5789dc8baedf9dcbe9c20918e2ba6..502705e0464981ecfc32233d22c747e14b3febf7 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -138,68 +138,73 @@ static int rps_default_mask_sysctl(const struct ctl_table *table, int write,
 static int rps_sock_flow_sysctl(const struct ctl_table *table, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct rps_sock_flow_table *o_sock_table, *sock_table;
+	static DEFINE_MUTEX(sock_flow_mutex);
+	rps_tag_ptr o_tag_ptr, tag_ptr;
 	unsigned int orig_size, size;
-	int ret, i;
 	struct ctl_table tmp = {
 		.data = &size,
 		.maxlen = sizeof(size),
 		.mode = table->mode
 	};
-	struct rps_sock_flow_table *o_sock_table, *sock_table;
-	static DEFINE_MUTEX(sock_flow_mutex);
 	void *tofree = NULL;
+	int ret, i;
+	u8 log;
 
 	mutex_lock(&sock_flow_mutex);
 
-	o_sock_table = rcu_dereference_protected(
-					net_hotdata.rps_sock_flow_table,
-					lockdep_is_held(&sock_flow_mutex));
-	size = o_sock_table ? rps_sock_flow_table_mask(o_sock_table) + 1 : 0;
+	o_tag_ptr = tag_ptr = net_hotdata.rps_sock_flow_table;
+
+	size = o_tag_ptr ? rps_tag_to_mask(o_tag_ptr) + 1 : 0;
+	o_sock_table = rps_tag_to_table(o_tag_ptr);
 	orig_size = size;
 
 	ret = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 
-	if (write) {
-		if (size) {
-			if (size > 1<<29) {
-				/* Enforce limit to prevent overflow */
+	if (!write)
+		goto unlock;
+
+	if (size) {
+		if (size > 1<<29) {
+			/* Enforce limit to prevent overflow */
+			mutex_unlock(&sock_flow_mutex);
+			return -EINVAL;
+		}
+		sock_table = o_sock_table;
+		size = roundup_pow_of_two(size);
+		if (size != orig_size) {
+			sock_table = vmalloc_huge(size * sizeof(*sock_table),
+						  GFP_KERNEL);
+			if (!sock_table) {
 				mutex_unlock(&sock_flow_mutex);
-				return -EINVAL;
-			}
-			sock_table = o_sock_table;
-			size = roundup_pow_of_two(size);
-			if (size != orig_size) {
-				sock_table =
-				    vmalloc(RPS_SOCK_FLOW_TABLE_SIZE(size));
-				if (!sock_table) {
-					mutex_unlock(&sock_flow_mutex);
-					return -ENOMEM;
-				}
-				net_hotdata.rps_cpu_mask =
-					roundup_pow_of_two(nr_cpu_ids) - 1;
-				sock_table->_mask = size - 1;
+				return -ENOMEM;
 			}
+			net_hotdata.rps_cpu_mask =
+				roundup_pow_of_two(nr_cpu_ids) - 1;
+			log = ilog2(size);
+			tag_ptr = (rps_tag_ptr)sock_table | log;
+		}
 
-			for (i = 0; i < size; i++)
-				sock_table->ents[i] = RPS_NO_CPU;
-		} else
-			sock_table = NULL;
-
-		if (sock_table != o_sock_table) {
-			rcu_assign_pointer(net_hotdata.rps_sock_flow_table,
-					   sock_table);
-			if (sock_table) {
-				static_branch_inc(&rps_needed);
-				static_branch_inc(&rfs_needed);
-			}
-			if (o_sock_table) {
-				static_branch_dec(&rps_needed);
-				static_branch_dec(&rfs_needed);
-				tofree = o_sock_table;
-			}
+		for (i = 0; i < size; i++)
+			sock_table[i].ent = RPS_NO_CPU;
+	} else {
+		sock_table = NULL;
+		tag_ptr = 0UL;
+	}
+	if (tag_ptr != o_tag_ptr) {
+		smp_store_release(&net_hotdata.rps_sock_flow_table, tag_ptr);
+		if (sock_table) {
+			static_branch_inc(&rps_needed);
+			static_branch_inc(&rfs_needed);
+		}
+		if (o_sock_table) {
+			static_branch_dec(&rps_needed);
+			static_branch_dec(&rfs_needed);
+			tofree = o_sock_table;
 		}
 	}
 
+unlock:
 	mutex_unlock(&sock_flow_mutex);
 
 	kvfree_rcu_mightsleep(tofree);
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 4/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_sock_flow_table

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Instead of storing the @mask at the beginning of rps_sock_flow_table,
> use 5 low order bits of the rps_tag_ptr to store the log of the size.
>
> This removes a potential cache line miss to fetch @mask.
>
> More importantly, we can switch to vmalloc_huge() without wasting memory.
>
> Tested with:
>
> numactl --interleave=all bash -c "echo 4194304 >/proc/sys/net/core/rps_sock_flow_entries"
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 5/7] net-sysfs: get rid of rps_dev_flow_lock

[Eric Dumazet]

Use unrcu_pointer() and xchg() in store_rps_dev_flow_table_cnt()
instead of a dedicated spinlock.

Make a similar change in rx_queue_release(), so that both
functions use a similar construct and synchronization.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/net-sysfs.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 07624b682b08b24da790d377f1deec4dc0a84269..52fcf7fa58a808e79c1a17c8719830bcfb7c1674 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1084,7 +1084,6 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 {
 	unsigned long mask, count;
 	struct rps_dev_flow_table *table, *old_table;
-	static DEFINE_SPINLOCK(rps_dev_flow_lock);
 	int rc;
 
 	if (!capable(CAP_NET_ADMIN))
@@ -1128,11 +1127,8 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 		table = NULL;
 	}
 
-	spin_lock(&rps_dev_flow_lock);
-	old_table = rcu_dereference_protected(queue->rps_flow_table,
-					      lockdep_is_held(&rps_dev_flow_lock));
-	rcu_assign_pointer(queue->rps_flow_table, table);
-	spin_unlock(&rps_dev_flow_lock);
+	old_table = unrcu_pointer(xchg(&queue->rps_flow_table,
+				       RCU_INITIALIZER(table)));
 
 	if (old_table)
 		call_rcu(&old_table->rcu, rps_dev_flow_table_release);
@@ -1161,8 +1157,8 @@ static void rx_queue_release(struct kobject *kobj)
 {
 	struct netdev_rx_queue *queue = to_rx_queue(kobj);
 #ifdef CONFIG_RPS
+	struct rps_dev_flow_table *old_table;
 	struct rps_map *map;
-	struct rps_dev_flow_table *flow_table;
 
 	map = rcu_dereference_protected(queue->rps_map, 1);
 	if (map) {
@@ -1170,11 +1166,9 @@ static void rx_queue_release(struct kobject *kobj)
 		kfree_rcu(map, rcu);
 	}
 
-	flow_table = rcu_dereference_protected(queue->rps_flow_table, 1);
-	if (flow_table) {
-		RCU_INIT_POINTER(queue->rps_flow_table, NULL);
-		call_rcu(&flow_table->rcu, rps_dev_flow_table_release);
-	}
+	old_table = unrcu_pointer(xchg(&queue->rps_flow_table, NULL));
+	if (old_table)
+		call_rcu(&old_table->rcu, rps_dev_flow_table_release);
 #endif
 
 	memset(kobj, 0, sizeof(*kobj));
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 5/7] net-sysfs: get rid of rps_dev_flow_lock

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Use unrcu_pointer() and xchg() in store_rps_dev_flow_table_cnt()
> instead of a dedicated spinlock.
>
> Make a similar change in rx_queue_release(), so that both
> functions use a similar construct and synchronization.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 6/7] net-sysfs: remove rcu field from 'struct rps_dev_flow_table'

[Eric Dumazet]

Remove rps_dev_flow_table_release() in favor of kvfree_rcu_mightsleep().

In the following pach, we will remove "u8 @log" field
and 'struct rps_dev_flow_table' size will be a power-of-two.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/rps.h    |  1 -
 net/core/net-sysfs.c | 11 ++---------
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/include/net/rps.h b/include/net/rps.h
index dee930d9dd38e0e975e78d938bc7adc96048b724..e900480e828b487c721b3ef392f4abb427ad442c 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -44,7 +44,6 @@ struct rps_dev_flow {
  */
 struct rps_dev_flow_table {
 	u8			log;
-	struct rcu_head		rcu;
 	struct rps_dev_flow	flows[];
 };
 #define RPS_DEV_FLOW_TABLE_SIZE(_num) (sizeof(struct rps_dev_flow_table) + \
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 52fcf7fa58a808e79c1a17c8719830bcfb7c1674..fd6f81930bc6437957f32206c84db87ee242fede 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1072,13 +1072,6 @@ static ssize_t show_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 	return sysfs_emit(buf, "%lu\n", val);
 }
 
-static void rps_dev_flow_table_release(struct rcu_head *rcu)
-{
-	struct rps_dev_flow_table *table = container_of(rcu,
-	    struct rps_dev_flow_table, rcu);
-	vfree(table);
-}
-
 static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 					    const char *buf, size_t len)
 {
@@ -1131,7 +1124,7 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 				       RCU_INITIALIZER(table)));
 
 	if (old_table)
-		call_rcu(&old_table->rcu, rps_dev_flow_table_release);
+		kvfree_rcu_mightsleep(old_table);
 
 	return len;
 }
@@ -1168,7 +1161,7 @@ static void rx_queue_release(struct kobject *kobj)
 
 	old_table = unrcu_pointer(xchg(&queue->rps_flow_table, NULL));
 	if (old_table)
-		call_rcu(&old_table->rcu, rps_dev_flow_table_release);
+		kvfree_rcu_mightsleep(old_table);
 #endif
 
 	memset(kobj, 0, sizeof(*kobj));
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 6/7] net-sysfs: remove rcu field from 'struct rps_dev_flow_table'

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Remove rps_dev_flow_table_release() in favor of kvfree_rcu_mightsleep().
>
> In the following pach, we will remove "u8 @log" field
> and 'struct rps_dev_flow_table' size will be a power-of-two.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

[PATCH v3 net-next 7/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_dev_flow_table

[Eric Dumazet]

Instead of storing the @log at the beginning of rps_dev_flow_table
use 5 low order bits of the rps_tag_ptr to store the log of the size.

This removes a potential cache line miss (for light traffic).

This allows us to switch to one high-order allocation instead of vmalloc()
when CONFIG_RFS_ACCEL is not set.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/netdev_rx_queue.h |  3 +-
 include/net/rps.h             | 10 -----
 net/core/dev.c                | 53 +++++++++++++++-----------
 net/core/net-sysfs.c          | 70 +++++++++++++++++------------------
 4 files changed, 67 insertions(+), 69 deletions(-)

diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
index cfa72c4853876c6fcb84b5c551580d9205f7b29d..08f81329fc11dc86767f9da661be8c7194dc1da2 100644
--- a/include/net/netdev_rx_queue.h
+++ b/include/net/netdev_rx_queue.h
@@ -8,13 +8,14 @@
 #include <net/xdp.h>
 #include <net/page_pool/types.h>
 #include <net/netdev_queues.h>
+#include <net/rps-types.h>
 
 /* This structure contains an instance of an RX queue. */
 struct netdev_rx_queue {
 	struct xdp_rxq_info		xdp_rxq;
 #ifdef CONFIG_RPS
 	struct rps_map __rcu		*rps_map;
-	struct rps_dev_flow_table __rcu	*rps_flow_table;
+	rps_tag_ptr			rps_flow_table;
 #endif
 	struct kobject			kobj;
 	const struct attribute_group	**groups;
diff --git a/include/net/rps.h b/include/net/rps.h
index e900480e828b487c721b3ef392f4abb427ad442c..e33c6a2fa8bbca3555ecccbbf9132d01cc433c36 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -39,16 +39,6 @@ struct rps_dev_flow {
 };
 #define RPS_NO_FILTER 0xffff
 
-/*
- * The rps_dev_flow_table structure contains a table of flow mappings.
- */
-struct rps_dev_flow_table {
-	u8			log;
-	struct rps_dev_flow	flows[];
-};
-#define RPS_DEV_FLOW_TABLE_SIZE(_num) (sizeof(struct rps_dev_flow_table) + \
-    ((_num) * sizeof(struct rps_dev_flow)))
-
 /*
  * The rps_sock_flow_table contains mappings of flows to the last CPU
  * on which they were processed by the application (set in recvmsg).
diff --git a/net/core/dev.c b/net/core/dev.c
index d4837b058b2ff02e94f9590e310edbcb06dad0f2..053a30a8c0ea4464d3b61c7dde8ad916eeef1c19 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4968,16 +4968,16 @@ EXPORT_SYMBOL(rps_needed);
 struct static_key_false rfs_needed __read_mostly;
 EXPORT_SYMBOL(rfs_needed);
 
-static u32 rfs_slot(u32 hash, const struct rps_dev_flow_table *flow_table)
+static u32 rfs_slot(u32 hash, rps_tag_ptr tag_ptr)
 {
-	return hash_32(hash, flow_table->log);
+	return hash_32(hash, rps_tag_to_log(tag_ptr));
 }
 
 #ifdef CONFIG_RFS_ACCEL
 /**
  * rps_flow_is_active - check whether the flow is recently active.
  * @rflow: Specific flow to check activity.
- * @flow_table: per-queue flowtable that @rflow belongs to.
+ * @log: ilog2(hashsize).
  * @cpu: CPU saved in @rflow.
  *
  * If the CPU has processed many packets since the flow's last activity
@@ -4986,7 +4986,7 @@ static u32 rfs_slot(u32 hash, const struct rps_dev_flow_table *flow_table)
  * Return: true if flow was recently active.
  */
 static bool rps_flow_is_active(struct rps_dev_flow *rflow,
-			       struct rps_dev_flow_table *flow_table,
+			       u8 log,
 			       unsigned int cpu)
 {
 	unsigned int flow_last_active;
@@ -4999,7 +4999,7 @@ static bool rps_flow_is_active(struct rps_dev_flow *rflow,
 	flow_last_active = READ_ONCE(rflow->last_qtail);
 
 	return (int)(sd_input_head - flow_last_active) <
-		(int)(10 << flow_table->log);
+		(int)(10 << log);
 }
 #endif
 
@@ -5011,9 +5011,10 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		u32 head;
 #ifdef CONFIG_RFS_ACCEL
 		struct netdev_rx_queue *rxqueue;
-		struct rps_dev_flow_table *flow_table;
+		struct rps_dev_flow *flow_table;
 		struct rps_dev_flow *old_rflow;
 		struct rps_dev_flow *tmp_rflow;
+		rps_tag_ptr q_tag_ptr;
 		unsigned int tmp_cpu;
 		u16 rxq_index;
 		u32 flow_id;
@@ -5028,16 +5029,18 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 			goto out;
 
 		rxqueue = dev->_rx + rxq_index;
-		flow_table = rcu_dereference(rxqueue->rps_flow_table);
-		if (!flow_table)
+		q_tag_ptr = READ_ONCE(rxqueue->rps_flow_table);
+		if (!q_tag_ptr)
 			goto out;
 
-		flow_id = rfs_slot(hash, flow_table);
-		tmp_rflow = &flow_table->flows[flow_id];
+		flow_id = rfs_slot(hash, q_tag_ptr);
+		flow_table = rps_tag_to_table(q_tag_ptr);
+		tmp_rflow = flow_table + flow_id;
 		tmp_cpu = READ_ONCE(tmp_rflow->cpu);
 
 		if (READ_ONCE(tmp_rflow->filter) != RPS_NO_FILTER) {
-			if (rps_flow_is_active(tmp_rflow, flow_table,
+			if (rps_flow_is_active(tmp_rflow,
+					       rps_tag_to_log(q_tag_ptr),
 					       tmp_cpu)) {
 				if (hash != READ_ONCE(tmp_rflow->hash) ||
 				    next_cpu == tmp_cpu)
@@ -5076,8 +5079,7 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		       struct rps_dev_flow **rflowp)
 {
 	struct netdev_rx_queue *rxqueue = dev->_rx;
-	struct rps_dev_flow_table *flow_table;
-	rps_tag_ptr global_tag_ptr;
+	rps_tag_ptr global_tag_ptr, q_tag_ptr;
 	struct rps_map *map;
 	int cpu = -1;
 	u32 tcpu;
@@ -5098,9 +5100,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 
 	/* Avoid computing hash if RFS/RPS is not active for this rxqueue */
 
-	flow_table = rcu_dereference(rxqueue->rps_flow_table);
+	q_tag_ptr = READ_ONCE(rxqueue->rps_flow_table);
 	map = rcu_dereference(rxqueue->rps_map);
-	if (!flow_table && !map)
+	if (!q_tag_ptr && !map)
 		goto done;
 
 	skb_reset_network_header(skb);
@@ -5109,8 +5111,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		goto done;
 
 	global_tag_ptr = READ_ONCE(net_hotdata.rps_sock_flow_table);
-	if (flow_table && global_tag_ptr) {
+	if (q_tag_ptr && global_tag_ptr) {
 		struct rps_sock_flow_table *sock_flow_table;
+		struct rps_dev_flow *flow_table;
 		struct rps_dev_flow *rflow;
 		u32 next_cpu;
 		u32 flow_id;
@@ -5130,7 +5133,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		/* OK, now we know there is a match,
 		 * we can look at the local (per receive queue) flow table
 		 */
-		rflow = &flow_table->flows[rfs_slot(hash, flow_table)];
+		flow_id = rfs_slot(hash, q_tag_ptr);
+		flow_table = rps_tag_to_table(q_tag_ptr);
+		rflow = flow_table + flow_id;
 		tcpu = rflow->cpu;
 
 		/*
@@ -5190,19 +5195,23 @@ bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index,
 			 u32 flow_id, u16 filter_id)
 {
 	struct netdev_rx_queue *rxqueue = dev->_rx + rxq_index;
-	struct rps_dev_flow_table *flow_table;
+	struct rps_dev_flow *flow_table;
 	struct rps_dev_flow *rflow;
+	rps_tag_ptr q_tag_ptr;
 	bool expire = true;
+	u8 log;
 
 	rcu_read_lock();
-	flow_table = rcu_dereference(rxqueue->rps_flow_table);
-	if (flow_table && flow_id < (1UL << flow_table->log)) {
+	q_tag_ptr = READ_ONCE(rxqueue->rps_flow_table);
+	log = rps_tag_to_log(q_tag_ptr);
+	if (q_tag_ptr && flow_id < (1UL << log)) {
 		unsigned int cpu;
 
-		rflow = &flow_table->flows[flow_id];
+		flow_table = rps_tag_to_table(q_tag_ptr);
+		rflow = flow_table + flow_id;
 		cpu = READ_ONCE(rflow->cpu);
 		if (READ_ONCE(rflow->filter) == filter_id &&
-		    rps_flow_is_active(rflow, flow_table, cpu))
+		    rps_flow_is_active(rflow, log, cpu))
 			expire = false;
 	}
 	rcu_read_unlock();
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index fd6f81930bc6437957f32206c84db87ee242fede..2ce011fae2490b3bd950cf8d9089e7d71cc0fd7a 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1060,14 +1060,12 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 static ssize_t show_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 					   char *buf)
 {
-	struct rps_dev_flow_table *flow_table;
 	unsigned long val = 0;
+	rps_tag_ptr tag_ptr;
 
-	rcu_read_lock();
-	flow_table = rcu_dereference(queue->rps_flow_table);
-	if (flow_table)
-		val = 1UL << flow_table->log;
-	rcu_read_unlock();
+	tag_ptr = READ_ONCE(queue->rps_flow_table);
+	if (tag_ptr)
+		val = 1UL << rps_tag_to_log(tag_ptr);
 
 	return sysfs_emit(buf, "%lu\n", val);
 }
@@ -1075,8 +1073,10 @@ static ssize_t show_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 					    const char *buf, size_t len)
 {
+	rps_tag_ptr otag, tag_ptr = 0UL;
+	struct rps_dev_flow *table;
 	unsigned long mask, count;
-	struct rps_dev_flow_table *table, *old_table;
+	size_t sz;
 	int rc;
 
 	if (!capable(CAP_NET_ADMIN))
@@ -1093,38 +1093,36 @@ static ssize_t store_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
 		 */
 		while ((mask | (mask >> 1)) != mask)
 			mask |= (mask >> 1);
-		/* On 64 bit arches, must check mask fits in table->mask (u32),
-		 * and on 32bit arches, must check
-		 * RPS_DEV_FLOW_TABLE_SIZE(mask + 1) doesn't overflow.
-		 */
-#if BITS_PER_LONG > 32
-		if (mask > (unsigned long)(u32)mask)
-			return -EINVAL;
-#else
-		if (mask > (ULONG_MAX - RPS_DEV_FLOW_TABLE_SIZE(1))
-				/ sizeof(struct rps_dev_flow)) {
-			/* Enforce a limit to prevent overflow */
+
+		/* Do not accept too large tables. */
+		if (mask > (INT_MAX / sizeof(*table) - 1))
 			return -EINVAL;
-		}
-#endif
-		table = vmalloc(RPS_DEV_FLOW_TABLE_SIZE(mask + 1));
+
+		sz = max_t(size_t, sizeof(*table) * (mask + 1),
+			   PAGE_SIZE);
+		if (sz <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
+		    is_power_of_2(sizeof(*table)))
+			table = kvmalloc(sz, GFP_KERNEL);
+		else
+			table = vmalloc(sz);
 		if (!table)
 			return -ENOMEM;
-
-		table->log = ilog2(mask) + 1;
+		tag_ptr = (rps_tag_ptr)table;
+		if (rps_tag_to_log(tag_ptr)) {
+			pr_err_once("store_rps_dev_flow_table_cnt() got a non page aligned allocation.\n");
+			kvfree(table);
+			return -ENOMEM;
+		}
+		tag_ptr |= (ilog2(mask) + 1);
 		for (count = 0; count <= mask; count++) {
-			table->flows[count].cpu = RPS_NO_CPU;
-			table->flows[count].filter = RPS_NO_FILTER;
+			table[count].cpu = RPS_NO_CPU;
+			table[count].filter = RPS_NO_FILTER;
 		}
-	} else {
-		table = NULL;
 	}
 
-	old_table = unrcu_pointer(xchg(&queue->rps_flow_table,
-				       RCU_INITIALIZER(table)));
-
-	if (old_table)
-		kvfree_rcu_mightsleep(old_table);
+	otag = xchg(&queue->rps_flow_table, tag_ptr);
+	if (otag)
+		kvfree_rcu_mightsleep(rps_tag_to_table(otag));
 
 	return len;
 }
@@ -1150,7 +1148,7 @@ static void rx_queue_release(struct kobject *kobj)
 {
 	struct netdev_rx_queue *queue = to_rx_queue(kobj);
 #ifdef CONFIG_RPS
-	struct rps_dev_flow_table *old_table;
+	rps_tag_ptr tag_ptr;
 	struct rps_map *map;
 
 	map = rcu_dereference_protected(queue->rps_map, 1);
@@ -1159,9 +1157,9 @@ static void rx_queue_release(struct kobject *kobj)
 		kfree_rcu(map, rcu);
 	}
 
-	old_table = unrcu_pointer(xchg(&queue->rps_flow_table, NULL));
-	if (old_table)
-		kvfree_rcu_mightsleep(old_table);
+	tag_ptr = xchg(&queue->rps_flow_table, 0UL);
+	if (tag_ptr)
+		kvfree_rcu_mightsleep(rps_tag_to_table(tag_ptr));
 #endif
 
 	memset(kobj, 0, sizeof(*kobj));
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH v3 net-next 7/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_dev_flow_table

[Kuniyuki Iwashima]

On Mon, Mar 2, 2026 at 10:14 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Instead of storing the @log at the beginning of rps_dev_flow_table
> use 5 low order bits of the rps_tag_ptr to store the log of the size.
>
> This removes a potential cache line miss (for light traffic).
>
> This allows us to switch to one high-order allocation instead of vmalloc()
> when CONFIG_RFS_ACCEL is not set.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

I like this idea :)

I wondered if the alignment could be by 4 bytes on 32-bit kernel
and I learned it's not thanks to long long ARCH_KMALLOC_MINALIGN.

Thanks !

Re: [PATCH v3 net-next 0/7] rfs: use high-order allocations for hash tables

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon,  2 Mar 2026 18:14:25 +0000 you wrote:
> This series adds rps_tag_ptr which encodes both a pointer
> and a size of a power-of-two hash table in a single long word.
> 
> RFS hash tables (global and per rx-queue) are converted to rps_tag_ptr.
> 
> This removes a cache line miss, and allows high-order allocations.
> 
> [...]

Here is the summary with links:
  - [v3,net-next,1/7] net: add rps_tag_ptr type and helpers
    https://git.kernel.org/netdev/net-next/c/42a101775bc5
  - [v3,net-next,2/7] net-sysfs: remove rcu field from 'struct rps_sock_flow_table'
    https://git.kernel.org/netdev/net-next/c/61753849b8bc
  - [v3,net-next,3/7] net-sysfs: add rps_sock_flow_table_mask() helper
    https://git.kernel.org/netdev/net-next/c/9cde131cdd88
  - [v3,net-next,4/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_sock_flow_table
    https://git.kernel.org/netdev/net-next/c/dd378109d20f
  - [v3,net-next,5/7] net-sysfs: get rid of rps_dev_flow_lock
    https://git.kernel.org/netdev/net-next/c/68b6394a220b
  - [v3,net-next,6/7] net-sysfs: remove rcu field from 'struct rps_dev_flow_table'
    https://git.kernel.org/netdev/net-next/c/b2cc61857e3c
  - [v3,net-next,7/7] net-sysfs: use rps_tag_ptr and remove metadata from rps_dev_flow_table
    https://git.kernel.org/netdev/net-next/c/a435163d3100

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html